Method for preventing overload in base station and base station system thereof

ABSTRACT

A base station in a mobile communications system is provided. The base station comprises a reception processing unit demodulating a reception signal; an interference level measuring unit measuring an interference level (ROT) of the reception signal by uniform time interval; and an interference level processing unit comparing a previously measured first interference level with a newly measured second interference level to selectively output the second interference level to a second processor.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of the Korean Application No.P2002-081722 filed on Dec. 20, 2002, the content of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method for preventing overloadin a base station of mobile communication system and more particularly,to a method to reduce network overload generated from the base stationin the process of measuring and transferring interference level in amobile communication system supporting high-speed data services.

[0004] 2. Discussion of the Related Art

[0005] 1xEV-DO is a high-speed data service developed by Qualcomm ofU.S.A. in the late 1990's. The 1xEV-DO (1x evolution-data only) systemadopts an intrinsic resource allocation method fitting the respectivelink.

[0006] A base station consecutively transmits pilot signals withconstant power in case of the forward link. The terminals in a cellmeasure the strength of the pilot signal to estimate channel status ofthe forward link. Once such an estimated channel status is reported tothe base station, a scheduler of the base station determines whether toallocate a forward link resource to a specific terminal according to theforward channel status reported by each of the terminals with time-sharefor each slot.

[0007] The scheduler basically operates to allocate the maximum numberof resources to the terminal with the best channel status. Thismaximizes total data throughput of the forward link for each cell.

[0008] Since the base station receives reverse pilot signals fromterminals scattered in the cell, it is unable to grasp the reverse linkcharacteristics related to the respective mobile terminals from thestrength of the reception signal received from each terminal through anantenna of the base station, unlike the case of the forward link.

[0009] Instead, to measure the strength of the entire reception signalsreceived through the reception antenna, the base station indirectlycontrols a load amount of the reverse link in a manner that the reverselink resource allocation of the same level is directed to the entireterminals based on the measured strength.

[0010] Each terminal in the cell receives reverse link load amount (datarate) direction bit [reverse activity bit (hereinafter abbreviated RAB)]as data rate increase/decrease information each slot from the basestation, and determines the data rate, by which the terminal willtransmit the data for the next frame, using probability based on thevalue of the RAB.

[0011] For example, if the RAB received from the base station directsthat the data rate should be lowered, each terminal determines withprobability whether to lower or maintain the data rate of the next frameaccording to the current reverse link data rate. If the base stationdirects to increase the data rate via RAB, the data rate of the nextframe is determined in the same manner.

[0012] Therefore, since the entire terminal in the cell adjust the datarate of the reverse link according to the RAB set by the base station,the RAB setup becomes a means for adjusting the load amount of thereverse link.

[0013] In one embodiment, the base station sets the RAB based on thefollowing algorithm. First, total reception power (Rx Power_Total)received via an antenna of a reception end of the base station andthermal noise power (Rx Power_Thermal) of the base station system aremeasured. Thermal noise power vs. reception signal power [rise overthermal (hereinafter abbreviated ROT)] corresponding to the differenceof the two values (i.e. interference level) is measured. And, the ROT iscompared to a reference value (ROT_Thresh), which was set up previously,to determine the RAB.

[0014] In this case, the reference value (ROT_Thresh) is commonly set upinto a level somewhat lower than a maximum interference level (ROT)acceptable by the base station and the measured ROT value is simplycompared to the reference value (ROT_Thresh) each slot to determine theRAB.

[0015]FIG. 1 illustrates a block diagram of a base station (BS) systemfor generating increase/decrease information of reverse link load amountin a base station of a mobile communication system and for transmittingit to each mobile station.

[0016] Referring to FIG. 1, a base station 10 according to a relatedart, which generates reverse activity bit (RAB) in a base station andtransmits it to a mobile station (not shown in the drawing). In oneembodiment, the base station 10 comprises a reception processing unit 11for receiving a transmission signal from a mobile station (MS) through areception antenna. The reception processing unit 11 demodulates thereceived signal. An interference level measuring unit 12 for measuringan interference level (ROT) for a signal transferred from the receptionprocessing unit 11 is also included.

[0017] A comparison unit 13 for comparing a value measured by theinterference level measuring unit 12 to a predetermined reference value(ROT_Thresh) is included in one embodiment. A RAB & transport channeldetermining unit 14 for determining a location of each mobile stationaccording to a RAB location in a channel slot by determining a RABaccording to a result of the comparison procedure are also included. Atransmission processing unit 15 for modulating a transmission signalcarrying the RAB outputted from the RAB & transport channel determiningunit 14 can be also included.

[0018] In a related art RAB transmitting method having theabove-explained configuration, the interference level measuring unit 12measures the interference level (ROT) of the signal transferred from thereception processing unit 11 by uniform time interval, and transfers itto the comparison unit 13. The comparison unit 13 then measures a loadof a reverse link by comparing the interference level (ROT) with thepredetermined reference value (ROT_Thresh) to transfer to the RAB &transport channel determining unit 14.

[0019] The RAB & transport channel determining unit 14 determines theRAB from the mobile station according to the comparison result of thecomparison unit 13 and then determines a location of each mobile stationaccording to the RAB in the channel slot to transmit to the transmissionprocessing unit 15. The transmission processing unit 15 then modulatesthe transmission signal, which carries transmission data rateinformation and the data rate increase/decrease information (RAB)outputted from the RAB & transport channel determining unit 14, andtransmits the modulated signal to the mobile station.

[0020] In this case, the RAB setup in the mobile communication systemshould be determined by slot unit. Specifically, since a RAB setupperiod determines a data rate by which the terminal will transmit datain a next frame over reverse link, it is preferable to be smaller than aframe length of a minimum reverse link. Hence, the interferencemeasuring unit 12 measures the interference level (ROT) by tick unitwhich is a minimum unit provided by a processor and transfers the valueto the comparison unit 13.

[0021] However, the interference level ROT measuring unit and thecomparison unit are built in separate processors, respectively. Sincemassive amount of data should be exchanged between the separateprocessors for unit time for the RAB setup, the related art brings aboutoverload in the base station.

SUMMARY OF THE INVENTION

[0022] In accordance with one embodiment of the invention, a method forpreventing overload in base station in a mobile communication system isprovided. The method comprises comparing interference levels measured inpredetermined time intervals; and selectively outputting a firstinterference level based on results of the comparing. The interferencelevels are measured in a reverse link.

[0023] In one embodiment, the comparing step comprises comparing aprevious interference level with a new interference level. The firstinterference level is a newly measured interference level. The firstinterference level is provided to a second processor, when a differencebetween the new and previous interference levels is greater than aspecific value.

[0024] When the new interference level is provided to the processor, theprevious interference level is replaced with the new interference level.A first processor performs the comparing and outputting steps, in oneembodiment.

[0025] The second processor is a channel card processor for controllingradio access according to mobile station and radio interfacespecifications. In some embodiments, the mobile communication system isa 1xEV-DO system or a 1xEV-DV system.

[0026] In accordance with another embodiment, a method for preventingoverload in base station, in a mobile communication system comprisesmeasuring a first interference level of a reverse link; measuring asecond interference level by uniform time interval; comparing the firstand second interference levels using a first processor; and outputtingthe second interference level to a second processor, when differencebetween the second and first interference levels is greater than athreshold.

[0027] The first interference level is replaced by the firstinterference level. In one embodiment, the measuring steps are performedin the first processor. The second processor is a channel card processorfor controlling radio access according to mobile station and radiointerface specifications.

[0028] In yet another embodiment, a base station in a mobilecommunications system is provided. The base station comprise a receptionprocessing unit demodulating a reception signal; an interference levelmeasuring unit measuring an interference level (ROT) of the receptionsignal by uniform time interval; and an interference level processingunit comparing a previously measured first interference level with anewly measured second interference level to selectively output thesecond interference level to a second processor.

[0029] The base station of claim 15, wherein the interference levelprocessing unit outputs the second interference level to the secondprocessor when a difference between the first and second interferencelevels is greater than a threshold.

[0030] The base station of claim 15, further comprising a memory unitfor storing the first and second interference levels. The interferencelevel measuring unit and the interference level processing unit areimplemented on a first processor. The second processor is a channel cardprocessor controlling radio access according to mobile station and radiointerface specifications.

[0031] The channel card comprises a comparison unit for comparing thesecond interference level outputted from the interference levelprocessing unit to a previously set reference value (ROT_Thresh); and aRAB generating unit generating a reverse link direction bit (RAB)according to a comparison result of the comparison unit.

[0032] These and other embodiments of the present invention will alsobecome readily apparent to those skilled in the art from the followingdetailed description of the embodiments having reference to the attachedfigures, the invention not being limited to any particular embodimentsdisclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and together with the description serve to explain theprinciples of the invention.

[0034]FIG. 1 illustrates a block diagram of a base station (BS) systemrequired for generating increase/decrease information of reverse linkload amount in a base station of a mobile communication system and fortransmitting it to each mobile station, in one or more embodiments.

[0035]FIG. 2 illustrates a block diagram of a base station systemaccording to one preferred embodiment of the present invention.

[0036]FIG. 3 illustrates a flowchart of a method for measuringinterference level in base station according to one embodiment of thepresent invention.

[0037]FIG. 4 illustrates a flowchart of a method for transmittinginterference level (ROT) to a channel card according to one embodimentof the present invention.

[0038] Features, elements, and aspects of the invention that arereferenced by the same numerals in different figures represent the same,equivalent, or similar features, elements, or aspects in accordance withone or more embodiments of the system.

DETAILED DESCRIPTION OF THE INVENTION

[0039] Referring to FIG. 2, a base station 20, according to anembodiment of the present invention, comprises a base station sectorconversion & up/down converter assembly (BUDA) 27 converting digital andanalog signals. A channel card 29 for radio access according to mobilestation and radio interface specifications, and a radio & channelprocessor (RCP) 28 for controlling the channel card 29 and controllingthe BUDA 27 and other RF equipments may be included. The BUDA 27comprises a reception processing unit 21 for demodulating a signalreceived via a reception antenna.

[0040] The RCP 28 comprises an interference level measuring unit 22measuring interference level for a signal transferred from the receptionprocessing unit 21 of the BUDA 27, an interference level processing unit23 comparing the measured interference level to an interference levelpreviously transferred to the channel card 29 to transmit acorresponding interference level (ROT) to the channel card 29 if adifference resulted from the comparison is equal to or greater than apredetermined value set previously, for example. A memory unit (notshown in the drawing) for storing the previous interference level and anew interference level, may be also included.

[0041] In one embodiment, the channel card 29 comprises a comparisonunit 24 for comparing the interference level transmitted from theinterference level processing unit 23 to a predetermined reference value(ROT_Thresh), a RAB & transport channel determining unit 25 determininga location of each mobile station according to a RAB location in achannel slot by determining reverse link load amount direction bit (RAB)according to result of the comparison. A transmission processing unit 26modulating a transmission signal carrying the reverse link load amountdirection bit (RAB) outputted from the RAB & transport channeldetermining unit 25 is included in a preferred embodiment.

[0042] Referring to FIG. 3, the BUDA 27 converts a received analogsignal to a digital signal and transmits it to the interference levelmeasuring unit 22. The RCP 28 generates an interrupt for interferencelevel (ROT) measurement (S30). The interference level measuring unit 22of the RCP 28 accordingly measures the interference level (ROT) of thesignal transferred from the reception signal processing unit 21 of theBUDA 27 (S31)

[0043] The interference level (ROT) can be measured by measuring totalreception power (Rx Power_Total) received via an antenna of thereception end of the base station and thermal noise power (RxPower_Thermal) of the base station system itself and by calculating adifference between the two values (if unit is dB)). The measuredinterference level (ROT) is stored in the memory unit in someembodiments.

[0044] A measured new interference level (ROT_(new)) is, for example,stored in the memory unit (S32). The new interference level (ROT_(new))and a previous interference level (ROT_(old)) having been transferred tothe channel card 29 are at least stored in the memory unit. It is amatter of course that the memory unit for storing the previous and newinterference levels (ROT_(old) and ROT_(new)) can be built separatelyfor the convenience of the system.

[0045] Referring to FIG. 4, the new interference level (ROT_(new))measured in the interference level measuring unit 22 is stored in thememory unit in one embodiment. The RCP 28 generates an interrupt to theinterference level processing unit 23 (S40). The interference levelprocessing unit 23 accordingly reads the new and previous interferencelevels (ROT_(new) and ROT_(old)) stored in the memory unit (S41) andthen judges whether the difference between the new and previousinterference levels (ROT_(new) and ROT_(old)) is greater than (or equalto) a specific value set previously (S42).

[0046] If the difference between the new and previous interferencelevels (ROT_(new) and ROT_(old))is not greater than the specific value,the measured new interference level (ROT_(new)) is not transferred tothe channel card 29. There is no data exchange between processors of theRCP 28 and channel card 29 so that data is not transmitted, wherebythere is no load due to the transmission of interference level (ROT) inthe base station system.

[0047] If the difference between the new and previous interferencelevels (ROT_(new) and ROT_(old))is greater than or equal to the specificvalue, the RCP 28 transmits the measured new interference level(ROT_(new)) to the channel card 29 (S43) and updates the memory unit tostore the measured interference level (ROT_(new)) into a new previousinterference level (ROT_(old′)) (S44), for example.

[0048] The comparison unit 24 of the channel card 29 compares theinterference level (ROT) transferred from the interference levelprocessing unit 23 to a predetermined reference value (ROT_Thresh) andtransmits the comparison result to the RAB & transport channeldetermining unit 25.

[0049] By determining the reverse link load amount direction bit RABaccording to the comparison result, the RAB & transport channeldetermining unit 25 determines the location of each mobile stationaccording to the RAB in the channel slot and then transfer it to thetransmission processing unit 26. The transmission processing unit 26modulates the transmission signal carrying the RAB outputted from theEAB & transport channel determining unit 25 and then transmits it to themobile station via transmission antenna.

[0050] The above-description of the embodiment is focused on the RABsetup method in the base station of 1xEV-DO system providing high-speeddata services. Yet, the present invention can be applied to 1xEV-DVsystem and the like providing high-speed packet data and voice servicesas well as other purposes including the RAB setup.

What is claimed is:
 1. A method for preventing overload in base station,in a mobile communication system, the method comprising: comparinginterference levels measured in predetermined time intervals; andselectively outputting a first interference level based on results ofthe comparing.
 2. The method of claim 1, wherein the interference levelsare measured in a reverse link.
 3. The method of claim 2, whereincomparing step comprises comparing a previous interference level with anew interference level.
 4. The method of claim 1, wherein the firstinterference level is a newly measured interference level.
 5. The methodof claim 3, wherein the first interference level is provided to a secondprocessor, when a difference between the new and previous interferencelevels is greater than a specific value.
 6. The method of claim 5,wherein when the new interference level is provided to the processor,the previous interference level is replaced with the new interferencelevel.
 7. The method of claim 1, wherein a first processor performs thecomparing and outputting steps.
 8. The method of claim 5, wherein thesecond processor is a channel card processor for controlling radioaccess according to mobile station and radio interface specifications.9. The method of claim 1, wherein the mobile communication system is a1xEV-DO system.
 10. The method of claim 1, wherein the mobilecommunication system is a 1xEV-DV system.
 11. A method for preventingoverload in base station, in a mobile communication system, the methodcomprising: measuring a first interference level of a reverse link;measuring a second interference level by uniform time interval;comparing the first and second interference levels using a firstprocessor; and outputting the second interference level to a secondprocessor, when difference between the second and first interferencelevels is greater than a threshold.
 12. The method of claim 11, whereinthe first interference level is replaced by the first interferencelevel.
 13. The method of claim 11, wherein the measuring steps areperformed in the first processor.
 14. The method of claim 11, whereinthe second processor is a channel card processor for controlling radioaccess according to mobile station and radio interface specifications.15. A base station in a mobile communications system, the base stationcomprising: a reception processing unit demodulating a reception signal;an interference level measuring unit measuring an interference level(ROT) of the reception signal by uniform time interval; and aninterference level processing unit comparing a previously measured firstinterference level with a newly measured second interference level toselectively output the second interference level to a second processor.16. The base station of claim 15, wherein the interference levelprocessing unit outputs the second interference level to the secondprocessor when a difference between the first and second interferencelevels is greater than a threshold.
 17. The base station of claim 15,further comprising a memory unit for storing the first and secondinterference levels.
 18. The base station of claim 15, wherein theinterference level measuring unit and the interference level processingunit are implemented on a first processor.
 19. The base station of claim15, wherein the second processor is a channel card processor controllingradio access according to mobile station and radio interfacespecifications.
 20. The base station of claim 19, wherein the channelcard comprises: a comparison unit for comparing the second interferencelevel outputted from the interference level processing unit to apreviously set reference value (ROT_Thresh); and a RAB generating unitgenerating a reverse link direction bit (RAB) according to a comparisonresult of the comparison unit.
 21. The base station of one of claim 15,wherein the mobile communication system is a 1xEV-DO system.
 22. Thebase station of one of claim 15, wherein the mobile communication systemis a 1xEV-DV system.